On the Mac, today you can use the built-in iCal and Address Book software as the way station, and then configure Entourage to sync with them (use the Sync Services pane of the Preferences dialog box). In iCal, you must create and use a calendar called Entourage for any entries you want synced to Exchange. (And Exchange calendar items will be placed in iCal in the Entourage calendar as well.) Then, with your iPhone physically connected and selected in iTunes' Devices list, open the Info pane to choose the calendars and contact sources to be synced. All three programs -- Entourage, iCal, and iTunes -- must be set up properly for this ménage à trois to work.
A tip for the 1.x software: In Entourage's preferences, choose whether to sync your server's calendar or your local calendar. If you change this setting, it's very likely that your calendar will stop syncing. It turns out the issue is in iCal: You'll see multiple Entourage calendars listed (one for each time you changed the setting in Entourage). Delete all but the "real" Entourage calendar (you can right-click on a calendar and choose Delete from the contextual menu).
Likewise, for Notes on the Mac, iTunes is the go-between as described for Exchange -- and you will need a separate app, such as Information Appliance Associates' PocketMac GoBetween, to make iCal and Address Book sync with Notes. Ironically, there doesn't appear to be a way to get calendar and address book data from Notes to the iPhone in Windows. If IBM follows up on its promise to ship a Notes client for iPhone, there'll be no need for a third-party app or other work-around.
You can, of course, access calendar and contact data today without connecting through the desktop by tapping Exchange or Notes Web access via the iPhone's Safari browser. Unfortunately, navigating those desktop-oriented pages even in the iPhone's fairly large screen makes this method a somewhat frustrating quick fix.
Securing the iPhone
The biggest issue for IT when it comes to the iPhone has been security, even with the availability of SSL authentication for securing e-mail connections. Make sure your Exchange or Domino server requires SSL and one of these SSL options: MD5 challenge-response, NTLM, or HTTP MD5 digest. The 1.x version of the iPhone also supports password-based SSL authentication, but that can be more easily spoofed than the other options.
Many enterprises want stronger protection than SSL provides, and so they typically use a VPN client -- or a BlackBerry or Motorola GoodLink server and its proprietary secured network -- as the conduit to safeguard all traffic with the iPhone.